The present invention relates to a method and to a humidifying device for assuring the maintenance of hydration of the contents of water impermeable packages or bags containing instruments and supplies to be sterilized by gas sterilization processes regardless of the ambient relative humidity of the environment surrounding the water impermeable packages or bags.
It has been widely recognized for many years by those skilled in the art and science of sterilization with gases such as ethylene oxide that the sterilization gas is more effective in killing microorganisms if those microorganisms are normally hydrated and, further, if the sterilization process is carried out in an atmosphere which contains at least 30% relative humidity. However, chamber-type ethylene oxide sterilizers, for example, heat their contents at the beginning of the sterilization cycle, thereby sharply reducing the relative humidity of the atmosphere in the chamber. To compensate for this, steam is injected into the chamber at the beginning of the sterilization cycle in an attempt to rehydrate dehydrated organisms and increase the hydration of the contents of the chamber prior to the introduction of the sterilizing gas. Provided that the contents of the chamber are packaged in water-permeable wrappings and enough water is introduced, this is a successful system.
However, when items to be sterilized are packaged in gas-permeable but water-impermeable wrappings, for instance, sealed in individual water-impermeable plastic bags, the contents of such packages will not be rehydrated by the injection of steam into the chamber and will be exposed to sharply declining relative humidity as the temperature of the chamber increases. Typically, relative humidity will decline by 50% for every 10.degree. C. rise in temperature.
The present invention relates to a method of assuring the maintenance of hydration of the contents of water-impermeable packages containing instruments and supplies during the gas sterilization process regardless of the ambient relative humidity. It further discloses the particular advantages of the invention as it pertains to gas diffusion-type gas sterilizers, for example, of the type marketed by H. W. Andersen Products, Inc. under the registered trademarks ANPROLENE.RTM. and STERIJET.RTM..
In the aforementioned gas diffusion-type gas sterilizers, items to be gas-sterilized are generally individually packaged in gas-permeable wrappings or packages. The user depends on these wrappings or packages to maintain the sterility of the items between the time they are removed from the sterilizer up to the time they are used. This often means that the wrappings or package must prevent the recontamination of its contents for years and through multiple shipments and rough handling. Water impermeable plastic films have proven to have many of the desirable features for use as the wrapping or packaging material for the above gas diffusion-type sterilizers.
More specifically, a prior art ethylene oxide gas sterilizer of this type is shown in FIGS. 1 to 3, wherein items to be sterilized are disassembled, washed, towel-dried and wrapped in a wrapping material such as cloth, paper or a plastic wrapping such as a proprietary plastic wrapping sold by H. W. Andersen Products, Inc. under the trademark SEAL AND PEEL.RTM.. The wrapped items to be sterilized are identified by the numeral 12, and these wrapped items 12 are placed in a gas diffusion membrane in the form of a water impermeable plastic bag 14 which is referred to as a liner bag 14. As shown in FIGS. 2 and 3, a gas-release mechanism 16 consists of liquid ethylene oxide sealed inside of a glass ampule 18 and packaged inside of a hermetically sealed gas diffusion membrane in the form of a plastic bag 20. The system is activated by snapping a prescored neck 22 of the ampule 18 without puncturing the gas diffusion membrane 20 surrounding it. This is achieved by placing ampule 18 in a protection sleeve 24 in membrane 20. After activation, the activated gas-release bag 16 is placed with the wrapped items 12 to be sterilized inside of the liner bag 14. The liner bag 14 is hermetically sealed around its contents (the wrapped items 12 to be sterilized and the activated gas-release bag 16) by means of a simple wire tie 26. The liner bag 14 is further enclosed in a ventilated container 28. During the sterilization cycle, which occurs at ambient room temperature, the liquid ethylene oxide in the sealed gas-release bag 20 boils, converting to pure ethylene oxide gas. The gas diffuses through the walls of the gas-release bag 20 and mixes with the air in th liner bag 14 in sufficient concentration to penetrate and sterilize the wrapped items 12. As the concentration of the gas increases in the liner bag 14, the ethylene oxide further diffuses through its walls into the surrounding container 28 from whence it is ventilated to the outside atmosphere. This gas sterilization system is marketed commercially by H. W. Andersen Products, Inc. under the registered trademark ANPROLENE.RTM. and is disclosed in U.S. Pat. No. 3,476,506, the entire contents of which are incorporated herein by reference.
Inasmuch as the liner bag 14 of such a system is substantially impermeable to water vapor, the relative humidity of the air in the liner bag 14 at the beginning of the sterilization cycle is maintained throughout the normal 12-hour exposure period. If the items to be sterilized have been washed with detergent and water as required, no dehydrated and hence no resistant microorganisms will be present. Effective use of the system, however, thus requires a minimum ambient relative humidity in the room where sterilization is performed. Present practice is to warn the user of such a sterilization system to measure the relative humidity in the room at the beginning of the sterilization cycle and not to proceed unless the relative humidity is at least 30%. This presents obvious limitations and disadvantageous considerations in the use of such a gas sterilization system.
Another prior art gas sterilizer, marketed commercially by H. W. Andersen Products, Inc. under the registered trademark STERIJET.RTM., is shown, for example, in FIGS. 4 and 5, where items to be sterilized 30 are prepared by washing and drying in the same manner as for the previously-described sterilization system. These items 30 are then wrapped in paper or cloth 31 and placed in an appropriate size liner bag 32. The liner bag 32 is placed over a spout 34 extending between jaws 36, 37 of a sterilizing device so that the spout 34 extends into the bag 32 and the lips 38 of the bag 32 extend between the jaws 36, 37. The jaw 36 is mounted on a pivotal arm assembly 27. A cycle number button coinciding with the number printed on the liner bag 32 is depressed t select the appropriate dose of gas, and a foot switch is pressed to start the cycle. Rubber-cushioned jaws 36, 37 close to hermetically seal the lips 38 of the bag 32 about the spout 34. Air is pumped from the bag 32 until the bag appears to be vacuum-tight around the enclosed items 30. An appropriate dose of gas is then injected into the bag 32 through the spout 34 via the conduit 35.
After the introduction of sterilant, the arm assembly 27 is pivoted clockwise slightly to close outer Jaws 44, 46 on the portion of the bag 32 therebetween. The inner jaws 36, 37 do not prevent the closing of the outer jaws 44, 46 because the inner jaws 36, 37 are made of resilient material which can be compressed as the outer Jaws 44, 46 are moved from the FIG. 4 position to a closed position shown in FIG. 5.
After closure of the outer jaws 44, 46, an impulse of electric current is passed through a resistance wire 42 imbedded in or just below the surface of lower jaw 46. The upper jaw 44, which may be made of heat resistant rubber, presses the bag down against the heating wire 42. The wire 42 rapidly heats to a temperature sufficient to fuse the bag but below the ignition temperature of the sterilant thereby forming a seal in the conventional manner of heat sealing. After a short pause, to assure that the seal is cooled, the jaws 36, 37 and 44, 46 open, releasing the bag 32.
The bag 32 containing the items 30 to be sterilized and the sterilizing gas is then placed in a heated and ventilated aerator where it remains for at least 12 hours. By way of example, the aerator may be heated to 50.degree. C. During this time, the gas sterilizes the contents of the bag 32 and then diffuses through the wall of the liner bag 32 and is evacuated by the ventilator. Since the material from which the bag 32 is fabricated is permeable to ethylene oxide and impermeable to air, the vacuum initially drawn through the spout 34 reappears as the ethylene oxide diffuses out of the liner bag 32, ziving the liner bag 32 a finished and a characteristic vacuum-tight appearance of a sterile package. A sterilizing system of the type shown in FIGS. 4 and 5 is disclosed in U.S. Pat. Nos. 3,516,223 and 3,630,665, the entire contents of which are incorporated herein by reference.
As with the system of FIGS. 1 to 3, the operator of the system of FIGS. 4 and 5 is admonished not to attempt to sterilize unless the ambient relative humidity is at least 30%. Unlike the system of FIGS. 1 to 3, whose sterilization cycle is carried out at ambient temperature, the package in the system of FIGS. 4 and 5 is placed in a heated aerator which raises the temperature of the package and causes the relative humidity in the package to fall approximately 50% for each 10 degrees rise in temperature. For example, a product packaged under ambient conditions of 30% relative humidity at 20.degree. C. will have its relative humidity reduced to about 4% at 50.degree. C.
Fortunately for the efficacy of the FIGS. 4 and 5 system, there is considerable inertia in the system itself such that it takes at least an hour for the package to reach its final temperature. During this time. the ethylene oxide injected directly into the package has time to kill the enclosed microorganisms. Nevertheless, the physics of the system leave much to be desired.